This invention relates to water responsive thermoplastic compositions and articles constructed thereof. This invention particularly relates to thermoplastic copolyester compositions useful for the manufacture of disposable articles such as disposable diapers and feminine napkins. More particularly, this invention relates to thermoplastic copolyester compositions that are useful as a raw material in the manufacture of nonwovens, barrier films or coatings and as well as for various improved hot melt adhesives compositions useful for incorporating hydrophilic features into disposable articles.
Currently in the nonwoven industry, with the exception of the pulp and super absorbent materials, disposable articles tend to be made of materials that are hydrophobic in nature. Water dispersible thermoplastic materials are gaining greater popularity as disposable article converters desire to incorporate hydrophilic features into their products.
WO 95/18191 teaches a water-dissipatable or dispersible adhesive composition useful in forming paper articles and other products that can be recycled through repulping in both neutral and alkaline media. The water-dispersible adhesive composition is preferably a hot melt adhesive that is a low molecular weight, branched copolyester containing a sulfonomer. Such polymers have recently become available under the tradename xe2x80x9cEastman AQxe2x80x9d copolyesters.
The xe2x80x9cEastman AQxe2x80x9d copolyesters are currently available in three experimental viscosity grades and one commercial viscosity grade, namely Eastman AQ 1350. Table I depicts typical physical property data of the neat copolyesters. In general, the neat copolyesters exhibits several deficiencies including cold flowability of the low molecular weight copolyesters, as well as poor sprayability, poor thermal stability and reduced water dispersibility of the higher viscosity materials.
The applicants have found that the xe2x80x9cEastman AQxe2x80x9d copolyesters, as well as similar water responsive copolyesters, have great utility in the nonwoven converting industry. When properly formulated, the disadvantages of the neat polyester can be overcome. Furthermore, the applicants discovered that it is possible to control the degree of water responsiveness such that the formulated adhesives may be useful for incorporating hydrophilic features into the substrates as well as the adhesives present yet not necessarily be water dispersible at one end of the spectrum, to using water dispersible copolyesters as a base raw material to make in-line substrates as well as adhesives to manufacture a completely flushable sanitary napkin or diaper at the other extreme.
When properly formulated, water responsive copolyesters are also suitable for adhesives compositions that improve acquisition and fluid management. Such adhesive compositions may be present to stabilize the core, improve the wicking of the core, for fixation of super absorbent polymers, or as a hydrophilic coating on a nonwoven. Additionally, water dispersible copolyesters have utility in formulating more traditional adhesive applications for construction, elastic attachment, or as garment attachment adhesives for securing a feminine napkin to an undergarment.
The present invention is a disposable article comprising at least two layers wherein at least one of said layers is a body fluid impermeable barrier having an interior and exterior surface and at least one second layer, wherein at least one of said second layers is a body fluid permeable cover attached to said interior surface of said barrier wherein at least one layer comprises a water dispersible copolyester. The disposable article may also optionally contain, an absorbent layer, or at least one tissue layer, or at least one elastomeric material, or at least one superabsorbent polymer material disposed between said barrier and cover, or at least one adhesive bonding at least one layer to an adjacent layer or material. The water dispersible copolyester may be present as a raw material in the manufacture of permeable covers such as nonwoven, body fluid impermeable barrier films, fastening systems for tapes or fastening systems such as Velcro(copyright), and elastomeric features such as elastic leg and waist attachments, as well as standing leg gathers. Furthermore, water responsive copolyesters may be present in various traditional adhesive compositions intended to bond such substrates as well as for adhesives that improve acquistion and fluid management. The use of the water dispersible copolyester may be for any one or all of these nonwoven applications as well as numerous combinations of such applications.
The improved hot melt adhesive composition comprises at least 25% of at least one water dispersible copolyester and up to about 75% of at least one ingredient selected from the group consisting of compatible polymers, tackifiers, plasticizers, and waxes. A solid plasticizer is a preferred plasticizer. Preferably, the copolyester has a viscosity less than about 40,000 cps at 177xc2x0 C., more preferably less than about 7,000 cps at 177xc2x0 C. To increase the strength of the thermoplastic composition, a copolyester having a viscosity of about 28,000 cps or greater at 177xc2x0 C. is combined with a copolyester having a viscosity less than about 7,000 cps at 177xc2x0 C. The improved hot melt adhesive is sprayable, resists cold flow, and exhibits good thermal stability.
Although the hot melt adhesives exemplified herein are targeted for various nonwoven applications, the hot melt adhesive compositions may also be employed in a wide varierty of other uses as are known in the art. Examples of such include water repulpable adhesives for bookbinding, case and carton sealing, bag sealing, roll wrapping and tissue plybonding, as well as remoistenable adhesives for envelope seals and other labeling applications. The inventive pressure sensitive adhesives described herein have been found to have particular utility for bonding to moist surfaces. This aspect is advantageous for bottle labeling as well as for medical applications for bonding to skin, provided the water dispersible copolyester has the proper FDA clearance for such applications.
The preferred ingredients of the adhesive composition is dependent on the intended use of the adhesive and will be exemplified in the examples set forth in the specification.